<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button id="btn">click</button>
<script>
const o = {}
btn.onclick = function() {
  o.age = 18
  console.log(o)
};

</script>
</body>
</html>
